Apparatus for photochemical dyeing



Oct. 20, 1953 EARAVICH APPARATUS FOR PHOTOCHEMICAL. DYEING 5 Sheets-Sheet 1 Filed Jan. 5, 1950 INVENTOR.

(mm/4P0 PW/m Oct.-. 20, 1953 E. RAVICH APPARATUS FOR PHOTOCHEMICAL DYEING 5 Sheets-Sheet 2 Filed Jan. 5, 1950 INVENTOR. ZZU/Vfl/PD A PW/ P a W n BY v NMWW' Oct. 20, 1953 E. RAVICH APPARATUS FOR PHOTOCHEMICAL DYEING Filed Jan. 5, 1950 5 Shams-Sheet 3 Tij.E-

INVENTOR. Lao/V4 0 Fay/cw Oct 2 0, 1953 L. E. RAVICH 2,655,302

APPARATUS FOR PHOTO CHEMICAL. DYEING med Jan. 5, 1950 5 Shets-Sheet 4 M N Q IN VEN TOR. Z0A44Pfi A PAW/CH @M M \Q 9dr. 2%, 1953 E. RAVICH APPARATUS FOR PHOTOCHEMICAL DYEING 5 Sheets-Sheet 5 Filed Jan. 5 1950 6 R I l I I I I I I I I I I I 1 I l l l l l I I c a @M w n w n a p. h M M 5 T 27 n w w a n 4w M W M W J .Q W 1 aw F-[I I I I l I Ilfi I l I I I I l l I l i I I I l I I ||I| w y llllllllllllllllllllllllllllll 2 n J n u m 2 m 3 m Fawn m a y l ,v u w u v fl Patented Oct. 20, 1953 APPARATUS FOR PHOTOCHEMICAL DYEI Leonard E. Ravich, New York, N. Y., assignor to Brown-Allen Chemicals, Inc., New York, N. Y., a corporation of New York Application January 5, 1950, Serial No. 136,980

13 Claims.

This invention relates to the dyeing of textile fabrics and other materials, and more particularly to an improved method and apparatus for photochemical dyeing of materials.

In my copending applications Serial Nos. 67,547 and 117,742, filed December 27, 1948, and September 24, 1949, respectively (both now abandoned), of which this application is a continuation-impart, I have disclosed photochemical processes for dyeing materials, such as fabrics, by applying to the material an oxidizable dyestuff and a photosensitizer, and then exposing the material to controlled light radiation to oxidize and precipitate the dyestuii". According to the earlier of said applications, an indigosol dyestuff is combined with a light-sensitizing agent selected from the group consisting of cyanines, cyanates and thiocyanates, such as carbocyanine, isocyanate, or ammonium thiocyanate, which provides a light-energy absorption span much greater than that of the indi gosol. The sensitizer serves to absorp and transform radiant energy from a wider band into energy of activation necessary for a rapid saponification reaction to occur, yielding the leuco form of the vat dye which is then oxidized rapidly to.

the insoluble colored dye form. The eifect of the sensitizer, therefore, is a catalytic rather than a chemical one, in that it supplies under the influence of light in the visible spectrum a much greater energy of activation per unit of time than is absorbed by the unsensitized indigosol (sensitive mainly to the low wave lengths of light). With the greatly increased energy of activation afforded by the sensitizer, the saponification reaction and oxidation, with resulting precipitation of the vat dye, occur practically instantaneously when a textile coated or impregnated with the light sensitized indigosol is exposed to light.

According to the disclosure of the above-mentioned application Serial No. 117,742, the process involves applying to the material an oxidizable dyestuff, a photosensitive per-salt, such as potassium persulfate, and a photosensitizer such as uranium acetate, uranium nitrate or other uranyl salt or other material which fiuoresces with a wave length similar to the uranyl salt under the action of the controlled light radiation to which the textile or other material is exposed. Thus, there is an absorption of radiated light energy by the uranyl salt and a formation of another energy level, with a subsequent transfer of this energy level to the potassium persulfate or other persalt. This causes an accelerated decomposition of the per-salt with the formation or" nascent oxygen, whereby the dyestuff is oxidized very rapidly and uniformly upon exposure of the material to the light radiation.

In the practice of these processes, the photochemical reaction is eifected rapidly under the influence of ultra-violet light radiation of high intensity and in the presence of moisture, and the present invention has for its principal object the provision of a method and apparatus by which the moisture can be provided effectively and expeditiously in a continuous photochemical dyeing operation.

According to the present invention, the fabric or other material to be dyed is impregnated or coated with a solution or solutions of the dyestuff and the light-sensitizer and is then subjected to an atmosphere of finely divided moisture particles, which is preferably provided by spraying water into a dye development chamber through which the fabric is conveyed. While the material is thus subjected to the atmosphere of moisture particles, it is exposed to intense ultraviolet light radiation by passing the light through this moist atmosphere to the material. In this way, the atmosphere of moisture particles or mist serves two functions. First, it distributes the moisture for the reaction uniformly and minutely throughout the light-exposed area of the material and in intimate contact therewith. Secondly, it serves as a cooling medium to prevent burning or scorching of the material under the intense radiation from the lightsource.

In the preferred practice of the invention, the fabric or other material on which the dyestuff and light-sensitizer have been applied is moved by a conveyor, such as a roller system, through a housing having a dye development chamber partly defined by a pair of opposed ultra-violet light-transmitting plates located in the housing, the fabric passing through the housing between the plates with the plane of the fabric parallel to but spaced from the plates. The light-transmitting plates are arranged between two opposed banks of ultra-violet lamps, each bank having reflectors facing the reflectors of the other bank. The housing is also provided with means for interposing moisture between the fabric and the light source or lamps, such means comprising spray nozzles for delivering liquid in finely divided moisture particles between the opposed light-transmitting plates, on both sides of the fabric. An air draft is induced, as by means of a suction pipe, along the rear faces of the reflectors to prevent overheating of the reflectors by the lamps, but the spaces between the reflectors and the light-transmitting plates are shielded from the air draft so that the lamps in these spaces can operate at relatively high temperature for maximum efficiency. The development chamber between the light-transmitting plates is also shielded from the air draft, whereby the atmosphere of moisture particles or mist is maintained under substantially non-turbulent con,- ditions. The light-transmitting plates are mounted in the housing so that they can be moved to permit access to the development chamber and the lamns.

For a better understanding. of the invention, reference may be had to the accompanying drawings, in which:

Fig. 1 is a diagrammatic view of a preferred form of the new apparatus;

Fig. 2 is a front elevational view of the housing containing the dye development chamber of the apparatus illustrated in Fig. 1;

Fig. 3 is an enlarged front elevational view, partly in section, of the upper part of the housing shown in Fig. 2;

Fig. 4 is a view similar to Fig. 3 but showing the lower part of the housing;

Fig. 5 is a side elevational view of the dye development housing, showing one of the lighttransmitting plates removed from the interior of the housing;

Fig. 6 is an enlarged vertical sectional view of one of the light-transmitting plates, showing details of the assembly of the plate components, and

Fig. 7 is a schematic View illustrating the electrical connections for the dye development lamps.

Referring to Fig. 1, the apparatus as there shown comprises a tank H3 orpadye having a chamber [0a containing the dissolved dyestuif. The fabric F to be dyed is supplied from a roll H, from which it passes continuously into the dye solution in chamber [0a and then upward between rollers [2 which squeeze the excesssolution from the fabric. Fromthe rollers l2, the fabric passes continuously to a second tankor quetsch [3 having a chamber l3a containing a solution of the dye sens-itizer. After passing through the photosensitizing solution in chamber l3 a, the fabricis drawn between rollers M which squeeze out the excess solution. The tanks [0 and I3 thusco-nstitute means for applying the dye and the dye photosensitizer, respectively, to the fabric F.-

Examples of the dye and photosensitizer solutionsare as follows:

Example I.Vat dyestuffs Dyc solution (chamber 10a) ..Twenty.grams.of a potassium tetrasulfatederived from 3,3i-dianthrahydroquinonazine, obtained by oxidizingv potassium sulfate of 3-amino-2+chloroanthraquinone (Indigosol Blue I. B C), are dissolvedin 800 cc. of water at 140 to 160 degrees Fahrenheit. To this is added 25 cc, of a ammonium thiocyanate solution and 4 grams of awetting agent, such as sodiumlauryl sulfonate.

Photosensitizer solutionl chamber 13a) .Fifty grams of ammonium persulfate and 0.05 gram of uranium acetate dissolved in 1000 cc. of water.

Example II.-Suljur dyestufis Dye solution (chamber 10a) .--Twelve grams of the dyestufi prepared from S-amino-earbazole converted into the O-mercaptan and condensed with chloranil (tetrachloroquinonel (Hydron Blue R')- aredissolved-in 100000. of water at- 158476 degrees Fahrenheit. To this is added 15 grams of sodium sulfide, 5 grams of sodium carbonate, and 1 gram of sodium hydroxide along with dispersing agents and materials for promoting the absorption of the dyestuff, such as sodium chloride or Glaubers salt.

Photosensitizer solution (chamber- 13w) .-Fifty grams of potassium persulfate'and 0.05 gram of uranium acetate dissolved in 1000 cc. of water at F.

Example III.-Diphenyl dyes Dye solution (chamber 10a) .-Forty grams of aminodiphenylamine (Diphenyl Black) are dissolved in 600 cc. of warm water containing 50 grams of lactic acid and 50 grams of acetic acid.

Photosensz'tieer solution (chamber 13a) .-Fifty grams of potassium persulfate and 0.05 gram of uranium acetate dissolved in 1000 cc. of water at 120 F.

In addition to or in place of the uranyli salts mentioned above, dye sensitizers may be used which increase the range of spectral sensitivity by absorbing light energy at all wave lengthsand transferring the energy to a level at which it' can decompose the persulfate solution. Among these dye sensitizers are the isocyanine dyes, such as ethyl red, the carbocyanines, including pinacyanol, and a number of others such as kryptocyanine and neocyanine. Formulations employing the dye sensitizers with or without the uranyl sensitizers in the per-salt solution are submitted below. The dyestuif formulae may be the same as previously described.

Example I V Potassium persulfate g 50 Pinacyanol g 0.005 Ethyl red g' 0.005 Water cc' 1000 Example V Ammonium persulfate- -g 50 Neocyanine g- 0.01 Water cc 1000 The fabric thus saturated with, the dye and photosensitizer solutions then passes through, a chamber in a housing l5; ofv the dyedevelopment apparatus. As shown, the fabric enters the housing [5 from the top between a pair of conveyor rolls I6 anddescends through the. central part of. the housing to the bottomwhere it passes between conveyor rolls ll. The fabric is maintained under tension as it descends from the rolls IE to the rolls. ILso that it is maintained in a predetermined position in the housing. From the rolls ll, the fabric moves outward at; the bottom of the housing. and passes to a tank 48 or quetsch having a chamber 18a containing a washing bath. As the fabric passes through this chamber, the unreacted dyestufif is washed from the fabric, which is then drawn upward between squeeze rolls IQ for removing the excess liquid; The fabric then passes to a roll 20 on which itis wound.

Referring now to Figs. 2' through 6, the housing l5 of the dye development apparatus comprises opposed sidewalls 22, a front wall 22a and a rear Wall 22b. The front wall'22a (Fig. 2) is provided with a rectangular opening which is normally closed by a door 23 hinged on the housing. The door has a handle 23a which can be swung back and forth to project or withdraw locking rods 23b slidably mounted on the door. The free'ends of the rods 23b are adapted, when the door is closed, to enter keepers 24 and 24a mounted on the front wall of the housing, so as to lock the door firmly in position for effecting an airtight seal.

The housing has a top 220 supporting a pair of spaced angle-ironmembers 25 which extend parallel to each other along the front and back of the housing and serve to mount the conveyor rolls [6. The latter are journalled between the members 25, and one of the rolls I6 is driven from a driving shaft [6a through a belt (6b. The lower rolls I! are journalled between front and rear members 26 extending between legs 21 which support the housing. One of the conveyor rolls I1 is driven from a shaft Ila through a belt 11b. The drive shafts [6a. and [1a are rotated at constant speed from a motor (not shown).

The housing I5 is open at the bottom, except for a partial bottom 22d extending along the sides of the housing from front to back. The central part of the housing interior communicates at the bottom with atmosphere through the open sides between the legs 21, as shown at 28 in Fig. 5. A perforated bottom plate 29 mounted below the housing and the conveyor rolls I! (Fig. 5) serves to permit drainage of a liquid condensate from the interior of the housin as will be described in greater detail presently.

Within the housing are opposed partitions 30 extending from front to back and forming directly above the partial bottom 22d 2. pair of closed chambers 3|. Lamp reactors 32 are arranged in two vertical rows in each of the chambers 3|, where they are mounted on the partition 39. The reactors are electrically connected to mercury-vapor or ultra-violet lamps 33 and 33a :arranged in a pair of opposed vertical banks in the space between the partitions 30. As shown particularly in Fig. 5, the lamps 33 and 33a are of the quartz tube type, the tubes extending horizontally in the housing from front to back. The two banks of lamps 33 and 33a are provided with configurated plates 34 and 34a, respectively, extending from the front to the back of the housing and forming individual reflectors for the lamps, the reflectors of one lamp bank being opposed to and facing the reflectors of the other bank. The

- reflector plates 34 and 34a may be secured to the rear wall 22b of the housing and serve to support the mercury vapor lamps within the elongated recesses formed by the individual reflectors. Between each reflector plate and the fabric F is an ultra-violet light-transmitting plate 35 which is spaced slightly from the adjacent reflectors. The two plates 35 are disposed vertically in the housing, where they extend in parallel spaced relation from front to back. Each plate 35, as

. shown particularly in Fig. 5, comprises a frame in which panels 35a of quartz are mounted, the

panels being held by angle-iron members 35b ex-.

tending across the frame from one side to the other. As shown in Fig. 6, the panels 35a in one horizontal row are seated on the inwardly extending horizontal leg of a member 35b, and a thin stainless steel strip 350 is welded to the outer vertical face of this member 35b and extends up-' ing horizontal part of the next lower angle-iron member 351). Thus, each horizontal row of panels is staggered with respect to the adjacent upper and lower rows. Since quartz plates are generally available in only small sections, I find that composite plates 35 of adequate area can be assembled conveniently in the manner described, to

make the composite plates substantially airtight.

The frame of each composite plate 35 is provided at the top with U-shaped brackets 35] on which rollers 35g are mounted. The rollers of each plate 35 are supported on a track 36 which extends from the rear of the housing through a movable section 226 forming part of the front wall of the housing. At their inner ends, the

tracks 36 are suspended from brackets 36a secured to the top 220 of the housing, and at their outer ends the tracks are suspended from the ceiling (not shown) by rods 36b. Thus, the composite plates 35 are suspended from the parallel tracks 36, on which they are adapted to be rolled independently of each other from the. in-

terior of the housing when the door 23 is opened, as shown in Fig. 5. When one of the composite plates is rolled from the housing along its track 36, the corresponding housing section 22c is moved outwardly in front of the plate and along the track; and when the plate is rolled back into the housing, the corresponding plate 226 is replaced to complete the closure of the front of the housing after the door 23 is closed. The plates 35 are guided at their lower edges by angle-iron members 31 supported between cross pieces 38 at the bottom of the housing.

It will be observed that the composite lighttransmitting plates 35 define between them a chamber 39, which may be referred to as the dye development chamber. The fabric F, guided by the conveyor rolls l6 and [1, passes vertically through the central part of the development chamber 39, which it enters through a slot 40 in the housing top 220. As the fabric passes through the chamber 39, its plane is parallel to the opposing plates 35 but spaced therefrom.

In the space between the fabric F and each plate 35 is a spray system comprising a liquid supply pipe 42 and branch pipes 42a and 42b of different lengths which extend inwardly into the chamber 39 from the lateral edge portions of the plate 35. The branch pipes 42a and 42b terminate in spray nozzles 420 which are adapted to distribute the liquid in a very fine spray through- -out the chamber 39 on both sides of the fabric.

As shown in Fig. 5, the main pipe 42 on each side of the fabric is mounted on the frame of the adjacent plate 35 by means of straps or brackets 43. A flexible hose (not shown) is connected to a nipple 42d at one end of each pipe 42 to supply the water or other liquid from a suitable source. It will be understood that the spray system forms from the spaces between the partitions 30 and the plates 35 to a manifold 46 (Fig. 5). fold 46 is connected to a suction pipe 41 for in- The maniducing an air draft through the open bottom of the housing and upward through the space between each reflector plate 34-3411 and the adjacent partition 33, as shown by the arrows in Figs. 3 and 4. By means of this forced air draft, the reflectors are prevented from being overheated by the lamps 3333a. Due to the close aceasoz spacing between the reflectors and the adjacent quartz plates 35 the lamps. are shieldedfrom the air draft so that they can operate at the relatively high temperature required for maximum emiciency; The air draft is excluded from the development chamber 39 by means of bafiles. 48. ex:- tending from the fronttothe rear of" the; housing along the upper partsv of the quartz plates 35; at opposite sides of the fabric F, as shown: in Fig. 3. In this way, the air draft induced by the. suction: pipe 41 is prevented from dispersing. the; fog or spray introduced intothe chamber 39.

The fabric is delivered to the upper conveyor rolls t6 over a guide roller 49 and is withdrawn from the dye development apparatus. at the bottom along a guide roller 50. In some1cases-,.however, it may be desirable to. convey the fabric through the housing from the bottom: to the top,

and so I provide additional guide rollers 4.9a. and 5021;. tobe used when the direction. of travet of the fabric is to be reversed, in which case; the fabric enters the housing: from: the lower con;- veyor rolls I1 and leaves the housing by way of the upper conveyor-rolls 1E.

The mercury vapor lamps 33':-33u may be electrically connected to their corresponding reactors-31 as illustrated in Fig. '7. As there shown, the lamps in each bank are divided into three sections, and the sections in the two banks are connected at opposite terminals by wires 5?;5:3 and 520-530,, respectively, leading to. a current source 53 for energizin the lamps.

In preparing the apparatus for operation, the door 23 is opened to enable the leading end of the fabric F to be drawn downward manually from the conveyor rolls ['5- through the development chamber 39 to the conveyor rolls H, from which the end of the fabric is: then passed along the guide roll 59 and the rollers associated with the washing tank l8, to the delivery roll 20. When the door 23- has been closed, the apparatus is ready tobe operated by starting the liquid flow to'the pipes-42 of thespray system, starting the conveyor rolls 1-6: and I1, and energizing the As the, fabric moves through. the housing [5, after receiving the dyeandphotosensitizer solutions from tanks. Li] and 13, it is subjected. on both. sides to an atmosphere of finely divided moisture. particles introduced into the development chamber 39 by the spray system. At the same time, it isexpose'd. on both sidesto the intense. light' from. the mercury vapor lamps 33- 3-312, which emit: light; radiation between 2200 and 750.0: angstrom units. The. ultra-violet light from; these lamps. (and: their reflectorsz) passes through the plates 35 and the confined atmosphere of moisture.particles,which form a. mist or fog; to theopposed sides of the fabric.. The atmosphere of mist or fog in. which the moving fabric. is thus enveloped provides the. moisture for the. photochemical reaction and also: enables the use of intense radiation without burning or scorching: the fabric,. which is preferably exposed to, a temperature no. higher than about 9().'l00

E. in chambertll; In thisway, an exposure peri- 06.. in the order of a few seconds or less is generally sufficient to decompose the photosensitive per-salt solution and thus yield the oxygen necessaryto oxidize the dyestuif and precipitate it as a; colored,, light-fast and; water-insoluble substanceon or. within the fibres; Accordingly, the fabric may bemoved rapidly through, the entire apparatus, from thesupply. roll I I to. the: delivery roll 20;, by, the conveyor comprising; the various 8 rollers; '20: permit observation of the fabric passing through the:- dye. devolpment. housing t5, the door 23' and. the: side walls 2-2 may be pro:- vided with port-holes, covered with; ruby-red Plexiglas shields-wand; 5G.

The quartz: panels 3.50. of, the light-transmitting plates: 35. are arranged with their vertical edges. offset: laterally from each other: along the fabric path, as shown in: Fig. 5. The vertical seams: between adjacentpanels are. thereby prevented from: cutting: ofi a. large part of the light radiation to. any portion. of. the fabric passing through. the, dye development. chambers, By mounting: the branch pipes" 42a; and 42b: of; the spray system in. lin with the horizontal seams between. the panels; 35a, the; pipes; are prevented from cutting ofil' any appreciable amount of: light radiating to the fabric.. While some of: the. light radiation is necessarily lostv int passing through the plates 35: and. the. artificial fog. created: its the dye development chamber, the amount small as. icompared to the. total radiation: from the lamps. The latter are selected to provide: animtense radiation, and. for this purpose I have found that General Electric: vapor lamps; of the type 30:-UA.-7 615-705 v1, 6.1v amps): are satisfactory, particularly when arranged: in. opposed banks as described and illustrated.

In conveyingthe fabric through the apparatus, some provision should. be made for maintaining the. fabric under substantially constant tension, in spite of shrinking or stretching of the fabric as it is beingprocessed. Since: devices: for counteracting changes in fabric: tension, whileit is. being conveyed by rollers, are welt known. I have. not disclosed. such adevice in: detail. However, I have illustrated generally in Fig. I. a pair of tension-compensating rollers. 58: and: 580.. as.- sociated with the dye and: sensitizer'tanks: t0; and I3, respectively, these rollers. being arranged tov move up. or' down. to. counteract. changes in the fabric tension. Similar tension-compensating devices. may be. located at. other: parts. of the apparatus. to prevent. excessive or insufficient: tension in the fabric during the processing.

The: condensate: resultingfrom theartificial fog in chamber39 is discharged through. the open bottom of the: housing and. through. the underlying-perforated. plate 29,.from which itpassesto asuitabledrain.

It is. to be understood that the invention is; not limited; to the dyeing: of fabrics. but. is applicable to: other materialsas welt.

I" claim 1.. Apparatus for treating textil'efabrics and other materials; to which: a photosensitive d ye has. been applied; which. comprises a pair of 0pposed ultra-violet light-transmitting plates, a conveyor for moving the material continuously in a. path between but spaced: from said plates, 2. source of ultra-violet light located: near each plate at the side thereof remote from: said path, aliquid supply pipe; and a spray system connected to said pipe-for introducing moisture particles between said. plates and having spray outlets located on each. side of the moving fabric between said; path thereof and the adjacent transmitting plate;

2;. Apparatus. according, to clainr 1-,, comprising also reflectors adjacent-the; light sources. and facing saidplates, and path.

3. Apparatus according; to claim. 1-,. comprising also reflectors adjacent the light: sources and facing said plates and path, the plates andreflectors forming. substantially closed. spaces for the light sources, and means for inducing an air draft along the reflectors outside said spaces.

4. Apparatus for treating textile fabrics and other materials, to which a photosensitive dye has been applied, which comprises a housing, ultra-violet lamps arranged in opposing banks in the housing, ultra-violet light-transmitting plates arranged in opposed relation in the housing between said banks and forming a passage between the plates, opposing plates in the housing forming reflectors for the lamps, said lamps and light-transmitting plates being located between the reflector plates, a conveyor for moving the material continuously along said passage in a path between but spaced from the light-trans: mitting plates, a liquid supply pipe, and a spray system connected to said pipe for introducing moisture particles into the spaces between said path and the light transmitting plates.

5. Apparatus according to claim 4, in which the reflector plates form with said light-transmitting plates substantially closed spaces for the lamps, the housing having side walls forming with each reflector plate an air passage behind the reflectors, and means for inducing an air draft through each air passage to cool the reflectors.

6. Apparatus according to claim 4, in which each light-transmitting plate includes a frame and light-transmitting panels supported in the frame with the panel edges offset laterally from each other along said path.

7. Apparatus according to claim 4, comprising also means for movably mounting the lighttransmitting plates in the housing, to permit access to said passage and lamps.

8. Apparatus according to claim 4, comprising also a spray system mounted on the light-transmitting plates and operable to introduce moisture particles into said passage.

9. Apparatus for treating textile fabrics and other materials, to which a photosensitive dye has been applied, which comprises a housing having openings at the top and bottom, rollers at the top and bottom of the housing for conveying the material through the housing in a vertical path, ultra-violet lamps arranged in opposing vertical banks in the housing, reflectors for the lamps and positioned in the housing to face said path in opposed relation, ultraviolet light-transmitting plates in front of the 10 reflectors and disposed at opposite sides of said path, a liquid supply pipe, and a spray system in the housing connected to said pipe for introducing moisture particles between said path and the plates.

10. Apparatus for dyeing lengths of textile fabrics and other materials, which comprises means for applying the dye and a dye photosensitizer to the material, a source of ultraviolet light, a conveyor for moving the material in a path from said applying means to the region of the light source to expose the material to said light, an ultra-violet light-transmitting plate interposed between the light source and said path but spaced from said path, a liquid supply pipe, and means connected to said pipe for introducing moisture particles into the space between said path and the plate and in contact with the material.

11. Apparatus according to claim 10, comprising also a housing forming a development chamber having inlet and outlet openings for the material, said housing containing the light source and said moisture interposing means.

12. Apparatus according to claim 10, comprising also a reflector adjacent the light source and forming with said plate a substantially closed space for the light source.

13. Apparatus according to claim 10, in which said moisture-introducing means are mounted on the light-transmitting plate, the apparatus also comprising a movable mount for said plate, whereby the plate and the moisture-introducin means are movable into and out of operative position relative to the material path.

LEONARD E. RAVICH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,271,790 Snelling July 9, 1918 1,310,511 Summers July 22, 1919 1,768,635 Schaffner July 1, 1930 1,881,310 Coatsworth Oct. 4, 1932 1,980,971 Campsie Nov. 13, 1934 2,206,611 Lantz July 2, 1940 2,214,365 Flynn Sept. 10, 1940 2,485,267 Ellner Oct. 18, 1949 2,499,153 Nicholson Feb. 28, 1950 

